Patent GB-746186-A (GB)
Title: Improvements in processes of photographic reproduction and in light-sensitive materials therefor
IPC: G03C8/28
Filed: 1953-05-01
Abstract: 746,186. Photographic light-sensitive material and reproduction transfer therewith. KODAK, Ltd. May 1, 1953 [May 3, 1952], No. 12183/53. Class 98 (2). A support bears a light-sensitive silver halide emulsion layer and an unsensitized unhardened layer of colloidal binder, such as gelatin or polyvinyl alcohol, having dispersed therein an agent for promoting image formation such as nuclei or a chemical precipitant for dissolved silver ions. The silver halide emulsion layer may contain a non-diffusing tanning developing agent, and between such layer and the support there may be present a layer containing a silver halide solvent or such in a form as of barium sulphite which liberates the solvent by action of an alkaline developer. Alternatively a layer of completely exposed silver halide emulsion containing a non-diffusing tanning developing agent, and if desired baryta, and a silver halide solvent, may lie between the silver halide emulsion layer arid the support. In use the material is exposed to an object or image, developed in the presence of silver halide solvent, in the developer or in the material itself, whereby a positive image is formed in the upper, unsensitized layer, and this is pressed onto an absorbent support as of paper to transfer a portion of the unsensitized layer containing the positive image thereto. Successive transfers may be made to obtain duplicate images. If desired the unsensitized colloidal binder layer which eventually contains the positive image may be applied after, instead of before, exposure. In example (1) a gelatino-silver chloride emulsion on paper stock is overcoated with a gelatin layer containing colloidal zinc sulphide, exposed, developed in a metal-quinol developer containing hypo and chlorobenzotriazole for approximately one minute and pressed onto typewriter paper to place a positive imagecontaining layer thereon. Urea is present in the developer to increase softness of the gelatin image. Example 2 uses, similarly, a hardened gelatino-silver chloride emulsion overcoated with a polyvinyl alcohol layer containing cadmium sulphide. In example (3) a paper support being a layer made with barium sulphite instead of the usual baryta or barium sulphate is provided with a gelatino-silver chloride emulsion containing 3: 4-dihydroxy diphenyl as non- diffusing developer and then a gelatin-zinc sulphide layer as of example (1) and is exposed and developed in an alkaline urea solution containing a high proportion of sodium carbonate to release sodium sulphite from the barium sulphite and form a positive image in the zinc sulphide layer, a stratum of which is transferred to a receiving support as in example (1). A fourth example also describes the paperbarium sulphite-emulsion-zinc sulphide layer assembly, with special features whereby successive fractions of the top, zinc sulphide, layer may be transferred to a receiving support with little tendency for all of the layers to transfer at once. Specifications 655,273, 655,275, 725,667, 745,445 and 746,174 are referred to.